Neutron-absorbing alloy

ABSTRACT

A neutron-absorbing alloy of the following composition in % by weight: INDIUM, BETWEEN 1 AND 20; SAMARIUM, BETWEEN 0.5 AND 15; HAFNIUM, BETWEEN 5 AND 18; NICKEL, THE BALANCE REQUIRED TO OBTAIN 100.

United States Patent [191 Portnoi et al.

[ 1 Dec. 2, 1975 NEUTRON-ABSORBING ALLOY 221 Filed: Jan. 16, 1974 211 Appl. No.: 433,854

[52] US. Cl. 75/170; 176/93 R [51] Int. Cl. C22c 19/00 [58] Field of Search 75/171, 170; 148/32, 32.5;

176/93 R, 93 BP 56] References Cited UNITED STATES PATENTS 3,832,l67 8/1974 Shaw et al. 75/170 Primary Examiner-R. Dean Attorney, Agent, or Firm-Robert E. Burns; Emmanuel J. Lobato; Bruce L. Adams [57] ABSTRACT A neutron-absorbing alloy of the following composition in by weight:

indium, between i and 20;

Samarium, between 0.5 and 15;

hafnium, between 5 and I8;

nickel, the balance required to obtain I00.

2 Claims, N0 Drawings NEUTRON-ABSORBING ALLOY The present invention relates to a neutron-absorbing alloy finding application in systems of automatic control and safety of nuclear reactors such as, for example,

thermal and intermediate reactors used for the generation of power and propulsion.

There is known a neutron-absorbing material comprising the following ingredients in by weight: silver, 80; indium, 15; cadmium, 5. Said material displays the following properties:

density, 10.17 g/cm";

melting point, 800 i 10C;

neutron capture efficiency (that of boron carbide with a density of 1.8 g/cm taken as unity), 0.1;

residual neutron capture efficiency, 0.3;

corrosion resistance in water at high temperature and pressure (up to 300C), 0.83 mg/dm in 24 hrs.

The known neutron-absorbing material displays a number of disadvantages. v

The material is in short supply because it is based on silver. Further, the material has a low capture efficiency in dealing with thermal and intermediate neutrons and its residual neutron capture efficiency is also low, the point being that resulting from the irradiation of the basic ingredient, i.e., silver, is cadmium and of indium is tin. The cadmium produces an isotope, cadmium l 14, which has a small cross section for neutron capture and for this reason the efficiency deteriorates continuously in operation.

Another disadvantage of the known material is it low corrosion resistance in water at a high temperature and pressure.

It is the primary object of the present invention to increase the absorption capacity of the alloy disclosed in dealing with thermal and intermediate neutrons.

Another object of the present invention is to increase the neutron capture efficiency of the alloy dislosed.

A further object of the invention is to increase the corrosion resistance of the neutron-absorbing alloy.

The primary and other objects of the present invention are attained by the fact that the neutron-absorbing alloy containing indium is, according to the invention, of the following composition in by weight: indium, between 1 and 20; samarium, between 0.5 and 15; hafnium, between 5 and 18; nickel, the balance required to obtain 100.

It is preferable to have a neutron-absorbing alloy of the following composition in by weight: indium, samarium, 8; hafnium, 13.5; nickel 68.5.

Experimental studies carried out with Ni-In, Ni-Sm and Ni-Hf systems to probe into their neutron capture efficiency have revealed that the efficiency of the Ni-In system approaches that of indium when the indium content is 50 by weight, the efficiency of the Ni-Sm system approaches that of samarium when the samarium content is by weight and in the Ni-Hf system when the hafnium content is 18 by weight. Further experiments have also shown that the introduction of hafnium, in an amount between 5 and 18 by weight into the alloy disclosed, assures high absorption capacity and provides for the maintenance of the neutron capture efficiency of a reasonably high order throughout the life-time of a reactor.

The neutron-absorbing alloy dislosed is melted in vacuum furnaces operating in an inert gas atmosphere under a pressure of 280 to 300 mm Hg. The sequence of events is as follows: loading of the charge consisting of nickel placed in a crucible and of indium, samarium and hafnium placed in a metering hopper; evacuation of the system and filling it with an inert gas under a pressure between 280 and 300 mm Hg; heating of the nickel to a temperature of 900 to 1,000C; continuous introducing indium, samarium and hafnium in succession; pouring of the alloy obtained into ceramic, metallie and other moulds at a temperature of 1,500" to 1,510C.

The alloy disclosed has a corrosion resistance which is 3 to 3.5 times that of the silver-based alloy. Exposed during a 3,000-hr corrosion test to the action of hot water at 350C and 168 atm, the alloy disclosed gave an increase in the weight amounting to a rate of 0.59 mg/md .24 hrs. At the same time, the known silverbased alloy corroded severely at a temperature of 300C (the rate of weight increase was 0.83 mg/dm .24 hrs) and failed to stand the corrosion at all at a temperature of 350C.

' The alloy disclosed has a high neutron capture efficiency in absorbing thermal and intermediate-neutrons and also displays a high residual neutron capture efficiency which is twice that of the known alloy.

The castability of the alloy allows to fabricate automatic control and safety rods in a variety of sizes with minimum tolerances for machining and the structural strength of the alloy assures good reliability of the control system in power thermal reactors.

The present invention will be best understood from the following examples of the neutron-absorbing alloy disclosed.

EXAMPLE 1 The neutron-absorbing alloy was of the following composition in by weight:

indium, 10;

samarium, 8;

hafnium, 13.5;

nickel, 68.5.

The sequence of events in preparing said alloy was as follows. The charge was loaded a crucible (nickel) and a metering hopper (indium, samarium and hafnium). The system was evacuated and then filled with an inert gas under a pressure of between 280 and 300 mm Hg. On heating the nickel to between 900 and 1,000C, half of the total amount of indium was added and the heating went of for another 5 to 8 minutes until a melt was obtained. Introduced into it was a nickel-samarium alloy and the rest of indium (indium forms an eutectic with nickel with a melting point of 914C). After a further 10 minutes of heating to enable the mixture to melt, the temperature of the melt was increased to between l,400 and 1,450C and the hafnium was added. At the final stage, the melt was heated to between 1,500 and 1,510C, kept at this temperature for a period lasting between five and seven minutes and then the alloy was poured into moulds.

The main properties of the alloy so obtained are tabulated in Table 1 given below.

EXAMPLE 2 The composition of the neutron-absorbing alloy in by weight was as follows:

indium, 1;

samarium, 0.5;

hafnium, 5;

nickel, 93.5.

Said alloy was obtained in the way described in Example The properties of the alloy are also tabulated in Table 1.

EXAMPLE 3 The composition of the neutron-absorbing alloy in by weight was as follows:

indium, 20;

samarium, l5;

hafnium, 18; 1O

nickel, 47.

Said alloy was obtained in the way described in Example l. The properties of the alloy are tabulated in Table 1.

Table 1 Known Alloy disclosed in silverbased Exam- Exam- Exam Properties alloy ple 1 ple 2 ple 3 1. Neutron capture effi- 0.7 0.82- 0.4 0.82- 20 ciency (that of B.C 0.83 0.83 taken as unity) 2. Residual neutron cap- 0.3 0.6 0.2 0.6

ture efficiency at end of reactor lifetime (that of B C taken as unity) 3. Density. g/cm 10.17 9.1- 9.0 9 7 I so Table l-contmued Known Alloy disclosed in silverbased Exam- Exam- Exam- Properties y ple 1 ple 2 ple 3 4v Corrosion resistance in water at 168 atm after 3000 hrs (increase in weight. mg/dm .24 hrs):

at 300C 0.83 0.21 0.2 0.7 at 350C fails to 0.59 0.47 0.98

withstand corrosion 5. Ultimate tensile 23-32 30-34 18-27 strength at 20C. kg/mm What is claimed is:

l. A neutron-absorbing alloy consisting essentially of the following ingredients in by weight:

indium, between 1 and 20;

Samarium, between 0.5 and 15;

hafnium, between 5 and 18;

nickel, the balance required to obtain 100.

2. A neutron-absorbing alloy as claimed in claim 1 consisting essentially of the following composition in by weight:

indium, 10;

samarium, 8;

hafnium, 13.5;

nickel, 68.5. 

1. A NEUTRON-ABSORBING ALLOY CONSISTING ESSENTIALLY OF THE FOLOWING INGREDIENT IN % BY WEIGHT: INDIUM, BETWEEN 1 AND 20, SAMARIUM, BETWEEN 0.5 AND 15, HAFNIUM, BETWEEN 5 AND 18, NICKEL, THE BALANCE REQUIRED TO OBTAIN
 100. 2. A neutron-absorbing alloy as claimed in claim 1 consisting essentially of the following composition in % by weight: indium, 10; samarium, 8; hafnium, 13.5; nickel, 68.5. 